1. Field of the Invention
The present invention relates to a hydraulic drive mechanism in a machine tool. More particularly, it relates to a hydraulic drive mechanism by which a cylinder for actuating a movable member adapted to reciprocate in a machine tool, such as milling machine, boring machine or universal machine tool, is supplied with pressure oil so as to be driven.
2. Description of the Prior Art
As conventional machine tools, there are a milling machine, a boring machine, a planing machine, a grinding machine, a drilling machine, etc. Further, the milling machine includes vertical and horizontal ones, while the boring machine similarly includes vertical and horizontal ones.
In a large-sized machine tool, for example, a large-sized milling machine, boring machine or planing machine, a table for placing a workpiece thereon is slidably disposed on the upper surface of a large-sized bed so as to extend in the lengthwise direction of the bed. Two columns which are perpendicular to the upper surface of the table are erected in the shape of gateposts on both the sides of the table in the widthwise direction thereof. Column guides are respectively mounted on the two columns so as to be vertically slidable. A cross girder is fixed between the column guides, and it is contrived so as to be vertically movable in the direction perpendicular to the upper surface of the table. In addition, a saddle which is slidable in parallel with the upper surface of the table is mounted on one side surface of the cross girder.
Besides, in the planing machine, a tool rest which is provided with a cutting tool holder being vertically movable is attached to the saddle, or the tool rest is slidably mounted on the cross girder instead of the saddle.
On the other hand, in the large-sized milling machine or the large-sized boring machine, a spindle head 39 of cylindrical shape whose axial direction intersects orthogonally to the sliding direction of the saddle is fixed to the saddle, a spindle guide is fitted in the inner circumference of the spindle head so as to extend axially of the spindle head, and a spindle is rotatably mounted in the spindle guide. Herein, the distal end of the spindle is provided with a cutting tool holder on which a tool, such as milling cutter or boring bar, for machining the workpiece placed on the upper surface of the table is set.
The various conventional machine tools are, in general, dedicated machine tools which function alone, respectively. Meanwhile, each of many workpieces to be machined requires machining processes by several sorts of machine tools, so that the different sorts of machine tools must be used in correspondence with the individual machining processes of the workpiece.
In a large workshop, accordingly, the various machining processes of the various workpieces can be coped with by installing the large number of various machine tools in the workshop. In a small workshop, however, the number of the various machine tools to be installed is limited, which has led to the problem that coping with many sorts of workpieces or machining operations is difficult. Especially, the large-sized machine tools are limited in the installation number even in the large workshop.
Further, the activity rates of the various machine tools become high in case of mass production. In case of multikind and small-quantity production, however, there has been the problem that the activity rate of each machine tool becomes low in spite of the necessity of the large number of various machine tools.
In order to eliminate this problem, therefore, a system capable of many sorts of machining operations with a single machine tool, for example, a universal machine tool or an NC machining center, has been developed.
The universal machine tool or the large-sized machine tool, such as the milling machine as well as the boring machine or the planing machine stated above, includes an increased number of movable members adapted to reciprocate, for example, the table, column guides, saddle or/and spindle.
According to the machine tool in the prior art, in order to actuate the respective movable members, feed screws are individually connected to motors being rotation drive means through clutches as well as brakes, and the respective members to be actuated are fixed to corresponding feed arms held in threadable engagement with the feed screws. Thus, the motors are rotated frontwards and reversely to rotate the feed screws and to move the feed arms axially of feed rods, whereby the movable members are reciprocatively actuated so as to machine a workpiece.
In the prior-art machine tool wherein the respective movable members are reciprocated by the rotations of the feed screws, the motors which are the rotation drive means of the movable members need to be individually disposed. This has posed the problems of a complicated structure and an increased manufactural cost.
As another problem, since the movable members are respectively moved by directly transmitting the rotations of the feed screws connected to the individual motors, the fine adjustments of the motions are structurally limited on account of the moments of inertia.
Moreover, for the purpose of machining the workpiece at high precision, the motions of the respective movable members need to be finely adjusted, and the feed speeds of the movable members must be kept low. In rendering the high- and low-speed motions of the movable members compatible, the respective movable members need to be connected to the individual motors through the clutches, the brakes and reduction gears. This has led to the problem that the whole system becomes complicated and large-sized.